The present invention relates to an electrostatic ink jet recorder and, more particularly, to an electrostatic ink jet recorder of the type controlling charged toner particles contained in ink by using electrophoresis.
An electrostatic ink jet recorder of the type subjecting ink containing charged toner particles to an electric field and ejecting the ink toward a recording medium on the basis of a Coulomb force acting on the particles is conventional. An ink jet recorder of this type includes an electrophoresis electrode for causing the toner particles to gather at ejection ports due to electrophoresis. A plurality of ejection electrodes each ejects the particles gathering at the associated ejection port. A counter electrode is located at the rear of the recording medium while facing the ejection ports. Auxiliary electrodes are so arranged as to intensify electric fields around the ejection electrodes.
The conventional recorder of the type described has the following problems (1) and (2) left unsolved.
(1) Circuitry for driving the ejection electrodes and auxiliary electrodes is scaled up. Specifically, a single driver must be assigned to each ejection electrode, and a single driver must be assigned to each two auxiliary electrodes. It follows that a multielement head having e.g., electrodes arranged in several ten arrays or a line head having electrodes arranged in several hundred to several thousand arrays needs a prohibitive number of drivers, scaling up drive circuitry. Moreover, an increase in the number of drivers increases the overall size and production cost of the recorder.
(2) Even when the same voltage is applied the ejection electrodes, the amount of toner particles ejected differs from one ejection electrode to another ejection electrode, resulting in dots each having a different shape on a recording medium. This is ascribable to scatters ascribable to the head production process, e.g., scatters in the configuration of the ejection electrodes and ejection ports, the position of the auxiliary electrodes relative to the ejection electrodes, and the distance between the ejection electrodes and the counter electrode. The ejection electrodes, for example, promote the concentration of electric fields more positively when provided with sharper tips, increasing the amount of particles to be ejected and the size of a dot on the recording medium. As the distance between a given ejection electrode and the associated auxiliary electrode or the counter electrode decreases, compared to the distance between another ejection electrode and the associated auxiliary electrode or the counter electrode, the size of a dot on the recording medium increases, and vice versa. Such a scatter in dot size is aggravated when the number of ejection electrodes is increased.
Technologies relating to the present invention are also taught in, e.g., Japanese Patent Laid-Open Publication Nos. 57-11058, 2-217253, 6-286130, and 8-1942.